I don't like the look of those, too high etc.

Maybe a space saver - hehe just kidding

Think you've gotta be a bit more bendy with your Y pipe. Like make it more of a T and go around the spare. As it's 1 pipe splitting into 2 pipes the same diameter the gas has got twice the volume to flow into so, in theory at least, making your Y more angular shouldn't impact performance.

Spider mounts don't do much to keep the weight & centre of gravity low. Only seen one on a bit of a show truck - it had the raising side steps etc. It looked like a Paris-Dakar wanna be with no visibility out of the rear window and the cargo space severely compromised. Also the 'sports' bar on these trucks are usually only held on to the top cap of the tray by 4 bolts. I wouldn't be surprised if the weight of a spare wheel on a spider mount to the sports bar started to rip off somewhere.